video: fbdev: pm2fb: avoid stall on fb_sync

pm2fb_sync is called when doing /dev/fb read or write.
The original pm2fb_sync wait indefinitely on hardware flags which can
possibly stall kernel and make everything unresponsive.
Instead of waiting indefinitely, we can timeout to give user a chance to
get back control.

Signed-off-by: Tong Zhang <ztong0001@gmail.com>
---
 drivers/video/fbdev/pm2fb.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

Hi Randy,
Thanks for the comment.
I currently have this problem on my machine.
I have submitted a revised patch -- which includes the console log.
Thanks!
- Tong

On Sat, Feb 20, 2021 at 6:33 PM Randy Dunlap <rdunlap@infradead.org> wrote:
>
> Hi--
>
> On 2/20/21 3:02 PM, Tong Zhang wrote:
> > pm2fb_sync is called when doing /dev/fb read or write.
> > The original pm2fb_sync wait indefinitely on hardware flags which can
> > possibly stall kernel and make everything unresponsive.
> > Instead of waiting indefinitely, we can timeout to give user a chance to
> > get back control.
>
> Is this a real problem or theoretical?
> Does someone still use this driver?
>
>
> > Signed-off-by: Tong Zhang <ztong0001@gmail.com>
> > ---
> >  drivers/video/fbdev/pm2fb.c | 29 ++++++++++++++++++++++++++---
> >  1 file changed, 26 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/video/fbdev/pm2fb.c b/drivers/video/fbdev/pm2fb.c
> > index 27893fa139b0..8578c64a0c54 100644
> > --- a/drivers/video/fbdev/pm2fb.c
> > +++ b/drivers/video/fbdev/pm2fb.c
> > @@ -183,12 +183,23 @@ static inline void pm2v_RDAC_WR(struct pm2fb_par *p, s32 idx, u32 v)
> >
> >  #ifdef CONFIG_FB_PM2_FIFO_DISCONNECT
> >  #define WAIT_FIFO(p, a)
> > +#define WAIT_FIFO_TIMEOUT(p, a) (0)
> >  #else
> >  static inline void WAIT_FIFO(struct pm2fb_par *p, u32 a)
> >  {
> >       while (pm2_RD(p, PM2R_IN_FIFO_SPACE) < a)
> >               cpu_relax();
> >  }
> > +static int inline void WAIT_FIFO_TIMEOUT(struct pm2fb_par *p, u32 a)
>
> drop      void       ^^^
> It's already "int".
> Did you compile this?
>
> > +{
> > +     int timeout = 10000;
> > +     while (pm2_RD(p, PM2R_IN_FIFO_SPACE) < a) {
> > +             cpu_relax();
> > +             if (--timeout==0)
>
> spaces around ==
>
> > +                     return 1;
> > +     }
> > +     return 0;
> > +}
> >  #endif
> >
> >  /*
> > @@ -1031,15 +1042,27 @@ static int pm2fb_blank(int blank_mode, struct fb_info *info)
> >  static int pm2fb_sync(struct fb_info *info)
> >  {
> >       struct pm2fb_par *par = info->par;
> > +     int timeout_sync = 10000;
> > +     int timeout_fifo;
> >
> > -     WAIT_FIFO(par, 1);
> > +     if (WAIT_FIFO_TIMEOUT(par, 1))
> > +             goto end;
> >       pm2_WR(par, PM2R_SYNC, 0);
> >       mb();
> >       do {
> > -             while (pm2_RD(par, PM2R_OUT_FIFO_WORDS) == 0)
> > +             timeout_fifo = 10000;
> > +             while (pm2_RD(par, PM2R_OUT_FIFO_WORDS) == 0) {
> >                       cpu_relax();
> > -     } while (pm2_RD(par, PM2R_OUT_FIFO) != PM2TAG(PM2R_SYNC));
> > +                     if (--timeout_fifo==0)
>
> spaces around ==
>
> > +                             goto end;
> > +             }
> > +             if (pm2_RD(par, PM2R_OUT_FIFO) == PM2TAG(PM2R_SYNC))
> > +                     break;
> > +     } while (--timeout_sync>0);
>
> spaces around >
>
> >
> > +end:
> > +     if ((!timeout_sync) || (!timeout_fifo))
> > +             printk_ratelimited(KERN_WARNING "pm2fb: sync timeout!\n");
> >       return 0;
> >  }
> >
> >
>
>
> thanks.
> --
> ~Randy

Hi Tong,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v5.11 next-20210219]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Tong-Zhang/video-fbdev-pm2fb-avoid-stall-on-fb_sync/20210221-070421
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git f40ddce88593482919761f74910f42f4b84c004b
config: i386-randconfig-s002-20210221 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-15) 9.3.0
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.3-229-g60c1f270-dirty
        # https://github.com/0day-ci/linux/commit/77b85e0ba17f78b0335bf283901691ec3942dec3
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Tong-Zhang/video-fbdev-pm2fb-avoid-stall-on-fb_sync/20210221-070421
        git checkout 77b85e0ba17f78b0335bf283901691ec3942dec3
        # save the attached .config to linux build tree
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=i386 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All error/warnings (new ones prefixed by >>):

>> drivers/video/fbdev/pm2fb.c:193:1: warning: 'inline' is not at beginning of declaration [-Wold-style-declaration]
     193 | static int inline void WAIT_FIFO_TIMEOUT(struct pm2fb_par *p, u32 a)
         | ^~~~~~
>> drivers/video/fbdev/pm2fb.c:193:19: error: two or more data types in declaration specifiers
     193 | static int inline void WAIT_FIFO_TIMEOUT(struct pm2fb_par *p, u32 a)
         |                   ^~~~


vim +193 drivers/video/fbdev/pm2fb.c

   183	
   184	#ifdef CONFIG_FB_PM2_FIFO_DISCONNECT
   185	#define WAIT_FIFO(p, a)
   186	#define WAIT_FIFO_TIMEOUT(p, a) (0)
   187	#else
   188	static inline void WAIT_FIFO(struct pm2fb_par *p, u32 a)
   189	{
   190		while (pm2_RD(p, PM2R_IN_FIFO_SPACE) < a)
   191			cpu_relax();
   192	}
 > 193	static int inline void WAIT_FIFO_TIMEOUT(struct pm2fb_par *p, u32 a)
   194	{
   195		int timeout = 10000;
   196		while (pm2_RD(p, PM2R_IN_FIFO_SPACE) < a) {
   197			cpu_relax();
   198			if (--timeout==0)
   199				return 1;
   200		}
   201		return 0;
   202	}
   203	#endif
   204	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Hi Tong,

On Sun, Feb 21, 2021 at 1:05 AM Tong Zhang <ztong0001@gmail.com> wrote:
> On Sat, Feb 20, 2021 at 6:33 PM Randy Dunlap <rdunlap@infradead.org> wrote:
> > On 2/20/21 3:02 PM, Tong Zhang wrote:
> > > pm2fb_sync is called when doing /dev/fb read or write.
> > > The original pm2fb_sync wait indefinitely on hardware flags which can
> > > possibly stall kernel and make everything unresponsive.
> > > Instead of waiting indefinitely, we can timeout to give user a chance to
> > > get back control.
> >
> > Is this a real problem or theoretical?
> > Does someone still use this driver?
>
> I currently have this problem on my machine.
> I have submitted a revised patch -- which includes the console log.

Your machine is "QEMU Standard"?
Can this happen on real hardware, too, or is this a deficiency in QEMU,
which should be fixed there?

Gr{oetje,eeting}s,

                        Geert